Spinal subdural hematoma (SDH) is a rare condition and can be caused by several factors. Concomitant cranial and spinal SDH is even much less common. We present a 77-year-old male patient with lower back pain, paraparesis, and urinary retention following a sudden onset headache. Imaging revealed concomitant cranial and spinal SDH related to cerebral venous thrombosis (CVT) associated with hemorrhagic venous infarct. Laboratory examinations were consistent with polycythemia vera. There was no history of trauma and previous cranial surgery. Brain angiography did not reveal any evidence of arteriovenous fistula or vascular malformation. Since lower back pain occurred shortly after the headache and there was no other reasonable explanation for spinal hemorrhage, we suppose that the mechanism of spinal SDH is the migration of blood from the intracranial compartment. Therefore, this is the first report of concomitant spinal SDH and cerebral hemorrhage associated with CVT in a patient with myeloproliferative disease.